A ROTATING DISK STUDY ON THE RATES OF CALCITE DISSOLUTION AT 25 DEGREES CENTIGRADE (CALCIUM CARBONATE, MASS TRANSPORT, REACTION MECHANISM)

The dissolution of calcite along the cleavage face {100} was studied at 25(DEGREES)C in a carbonate solution of constant supporting electrolyte concentration and partial pressure of carbon dioxide. Rates of reaction were studied as a function of pH exposed surface area of calcite and rotational speed of the disk. The rotating disk method provided a uniformly accessible surface for the reconstruction of concentration gradients from the overall rates of dissolution.;In the interpretation of transport controlled kinetic data, it was important to take into account the effects of equilibrium reactions on the mechanism of transport. The extent to which the presence of homogenous reactions increase the overall mass transfer rates above values for purely physical diffusion were investigated as a function of the hydrodynamic fluid flow condition, the bulk solution pH and partial pressure of carbon dioxide.;The kinetic data suggested that the dissolution of calcite was controlled simultaneously by a surface reaction and by subsequent mass transport into the bulk of the solution. The gradation between transport and chemically controlled rates of dissolution was derived from a second order surface reaction rate low correlated to the mass flux and activity of hydrogen ions at the solution/calcite interface.